This invention relates to pumps and in particular to positive displacement hydraulic pumps of the expansible chamber type. Manual hydraulic pumps which are not reversible have existed for a long time. Numerous other positive displacement pumps also exist but they are of more complex construction and although sometimes capable of manual or reversible operation were not designed or intended for either. This invention is intended to satisfy the need for a low-cost manually operated, reversible, positive-displacement hydraulic pump of simple construction. Used in a hydraulic vise, hydraulic press, or in applications where large forces are necessary to precisely position machinery or pieces of work, this pump is capable of developing both high pressures and small displacements with greater accuracy and less actuating force than are possible by non-hydraulic mechanical means alone.
A number of previous patents, listed below, disclose pumps nearest in function to the pump here presented but not of similar design nor based upon the same principle of operation.
______________________________________ U.S. Pat. No. Patentee Date of Patent ______________________________________ 720,872 S. E. Alley 11/08/02 1,691,744 W. B. Van Arsdel 5/13/25 1,719,693 H. Ernst 9/15/27 1,799,449 G. F. Woelfel 3/01/28 1,819,285 W. Fourness 2/20/28 2,806,431 E. Woydt 2/10/56 3,057,301 J. M. J. Varga 12/13/60 ______________________________________
Alley discloses what appears to be the first use of cam-actuated sliding valves. Two valves are used instead of one, operated by separate cams.
Van Arsdel discloses the use of two pistons and a single two-way slide valve but uses separate mechanisms for actuation of the pumping members and valve.
Ernst, like Van Arsdel, discloses the use of a two-way inlet and discharge slide valve but actuated by a crank which is separate from the pumping member crank.
Woelfel discloses cam actuated slide valves and crank operated pistons.
Fourness discloses, in a compressor, cam operated slide valves and cam operated pistons, using separate cams.
Woydt discloses a cam actuated piston and a single slide valve operated by an arrangement of gears, chains, and sprockets.
Varga discloses a single cam which directly actuates a piston but operates through a rocker mechanism to actuate the slide valve in such a manner as to achieve a variable stroke pump.
None of the above patents discloses a pump which is intended to be either reversible or manually operated. None of the above patents discloses a pump design which is based upon the same operating principle, which is as simple, or has as few moving parts as the pump here disclosed. None of the above patents discloses a pump which would be of such economical manufacture and maintenance as the one here disclosed.